1. Field of the Invention
The present invention relates to a fuel injection valve.
2. Description of Related Art
A fuel injection valve supplies drive current to a coil to generate a magnetic attraction for attracting a movable core to a fixed core. Thus, a valve member lifts with the movable core, and the fuel injection valve injects fuel. In such a fuel injection valve, it is required to increase a range (dynamic range) of an energizing period, during which an injection quantity can be controlled with high accuracy. In order to increase the dynamic range, it is necessary to control the injection quantity with high accuracy specifically when the energizing period is short. Therefore, valve opening response and valve closing response should preferably be improved.
However, movement of the movable core in a valve opening direction will be hindered and the valve opening response will be deteriorated if a pressure in a facing space formed between the fixed core and the movable core increases when the coil is energized and the fixed core attracts the movable core.
Also, movement of the movable core in a valve closing direction will be hindered and the valve closing response will be deteriorated if the pressure in the facing space decreases when the coil is de-energized and the movable core separates from the fixed core.
Therefore, in a fuel injection valve disclosed in JP-A-H08-506876, a protrusion is provided on a surface of the fixed core or the movable core on a side on which the fixed core and the movable core face each other. Thus, a contact area on which the fixed core and the movable core contact is reduced. Accordingly, the hindrance of the pressure in the facing space to the movement of the movable core is inhibited when the valve is opened or closed. Thus, the valve opening response and the valve closing response can be improved.
However, the pressure in the facing space increases or decreases when the valve is closed or opened even if the contact area between the fixed core and the movable core is reduced. Therefore, the movement of the movable core is still hindered when the valve is opened or closed. As a result, the valve opening response and the valve closing response cannot be improved sufficiently.